JP4742041B2 - Liquid metal ion source and method for controlling a liquid metal ion source - Google Patents

Description

Field of Invention

  The present invention relates to a liquid metal ion source and a method for controlling these liquid metal ion sources.

Background of the Invention

  [02] Focused ion beam (FIB) systems are known. FIB systems are commonly used for die milling and cross sectioning. The object engraved or cut is usually analyzed by an inspection device (scanning electron microscope (SEM)) in order to detect defects. The FIB system can also be used to generate FIB images.

  [03] Various configurations of ion sources as well as voltages and electrodes are known. Some of these configurations are described in U.S. Pat. No. 6,459,082 to Sugiama et al., U.S. Pat. No. 6,458,082 to Sakaguchi, U.S. Pat. No. 5,153,440 to U.S. Pat. . Said patent is incorporated herein by reference. US Pat. No. 6,472,881 describes a liquid metal ion source and a method for measuring the flow impedance of the liquid ion source. US Pat. No. 5,110,533 describes a method for controlling a liquid metal source with analog feedback and digital CPU control. US Pat. No. 5,153,440 describes a method for stabilizing operation for a liquid metal ion source. The US Pat. No. 6,458,081 describes a focused ion beam system.

  [04] Also, an FIB system effective for generating an FIB image has at least one detection device and an image processor. Typically, the ion source, FIB system, and ion beam deflector are placed in a column commonly referred to as an FIB column. The detection device can also be placed in a FIB column.

  [05] The SEM image illuminates an object with an electron beam, collects signals resulting from electron beam mutual interference with at least a portion of the object, and processes the collected signals. FIB images are generated in a similar analog manner except that the object is illuminated with a focused ion beam.

  [06] Separate SEM and FIB tools are quite common, but systems including both FIB and SEM systems are also available. These hybrid systems are known as FIB / SEM systems. The SEM portion of the hybrid tool facilitates inspection of the surface of the inspection object (eg, the surface of a multilayered die). The FIB portion of the hybrid system facilitates surface carving and inspection exposure of the inner layer. Usually, after the FIB has carved the die, the SEM is used to inspect the revealed layer and to further analyze the die carved for detection. Two prior art FIB / SEM systems are FEI's XL860 dual beam workstation or SEM Vision G2 from Applied Materials, Inc., Santa Clara.

  [07] XL860 includes FIB and SEM columns, which are angularly positioned with respect to each other, but SEM vision G2 includes substantially parallel SEM and FIB columns.

  [08] Typically, focused ion beams are used to carve objects at regular intervals spaced apart from each other. Usually, once a wafer is carved or more specially carved, it is inspected by SEM or other tools.

  [09] Each liquid metal ion source has a predetermined amount of ions to supply. Thus, once the amount is supplied, the liquid metal ion source must be placed or replenished. The exchange is time consuming and expensive. In certain situations, the replacement or refilling procedure of the liquid metal ion source requires that the FIB chamber be opened, which is the time period during which the chamber's vacuum level (many levels greater than 2) must be maintained. It is a waste. Also, opening the FIB column may expose it to contaminants.

  [10] There is a need to provide efficient systems and methods for improved utilization of liquid metal ion sources.

Summary of the Invention

  [11] The present invention provides a system and method for reducing ion emission during idle periods.

  [12] The present invention provides a system and method for substantially eliminating ion emission during idle periods while the transition between idle and active modes is rapid.

  [13] According to embodiments of the present invention, the properties of the ion optics are hardly affected (or not at all) due to the transition between idle mode and active mode.

  [14] According to one embodiment of the present invention, one or more voltages supplied to one or more corresponding electrodes are substantially unchanged during mode transition, but supplied to one or more other electrodes. One or more voltages are changed.

[15] The present invention provides a method for controlling a liquid metal ion source, the liquid metal ion source comprising a tip of a first electrode and a second electrode, the method comprising: (i) a first voltage level Maintaining a first electrode within a range, maintaining a second electrode within a second voltage level range, and extracting metal ions formed at a tip of the liquid metal ion source during active mode operation of the liquid metal ion source When;
(Ii) maintaining the first electrode within the third voltage level range, maintaining the second electrode within the fourth voltage level range, substantially extracting metal ions from the tip during idle mode operation of the liquid metal ion source; And a step of reducing automatically. The third voltage level range and alternatively or additionally, the fourth voltage level range does not include a zero voltage level. The range of the first voltage level is different from the range of the third voltage level.

  [16] The present invention relates to a liquid metal ion source: a tip; a first electrode and a second electrode; a controller, formed at the tip of the liquid metal ion source during active mode operation of the liquid metal ion source In order to maintain the first electrode in the first voltage level range and to maintain the second electrode in the second voltage level range so as to extract the metal ions to be extracted, the liquid metal ion source is further in idle mode operation. At least one power source to maintain the first electrode in a third voltage level range and to maintain the second electrode in a fourth voltage level range so as to substantially reduce extraction of metal ions from the tip. And coupled to the controller. At least one of the third voltage level range and the fourth voltage level range does not include a zero voltage level, and the first voltage level range is different from the third voltage level range.

  [17] According to an embodiment of the present invention, the first electrode may be an extraction or suppression electrode.

  [18] According to an embodiment of the present invention, the third voltage level range may include a voltage level lower than the non-extracted voltage level by a first voltage difference.

  [19] According to various embodiments of the present invention, some voltage level ranges are different from each other. For example, the upper end of the first voltage level range is higher than the upper end of the third voltage level range, and / or the upper end of the fourth voltage level range is higher than the upper end of the second voltage level range.

  [20] According to embodiments of the present invention, the transition between the idle mode and the active mode does not substantially change the ion optical properties of the ion optics located downstream of the liquid metal ion source.

  [21] According to embodiments of the present invention, the transition between idle mode and active mode is rapid. It takes less than a minute and even a few seconds.

  [22] According to an embodiment of the present invention, ions provided at the tip are maintained in liquid form during idle mode.

  [23] According to an embodiment of the present invention, the transition step between the idle mode and the active mode is followed by a stabilization step of ion extraction from the tip. The stabilizing step may include measuring a flow of ions extracted from the tip, and changing a voltage level of a voltage supplied to one or more electrodes.

  [24] According to embodiments of the present invention, the transition between idle mode and active mode does not involve reheating of the liquid metal ion source.

  [25] In order to understand the present invention and know how it can actually be carried out, preferred embodiments will now be described with reference to the accompanying drawings, using only non-limiting examples.

Detailed description of the drawings

  [29] The FIB system 10 is described in FIG. The FIB system 10 includes: (i) an ion source for generating an ion beam (eg, a liquid metal ion source 20); (ii) a plurality of electrodes (eg, for extracting ions from the liquid metal ion source 20) Electrode 30 and a suppression electrode 40 that adjusts the focused electric field strength at the tip of the liquid ion source 20 so that the desired ion beam current is emitted from the liquid metal ion source); (iii) a plurality of power supply units (eg, FIB system) Extraction power supply 32 and suppression power supply 42 FIB system 10 for supplying voltages to 10 different components, and respective extraction electrodes 30 and suppression electrodes 40); (iv) ion optical components (eg, FIB) A lens system 50 and an ion beam deflector 60). The FIB lens system 50 can focus the ion beam to provide a focused ion beam. The ion beam deflector 60 can deflect the focused ion beam. Typically, the FIB system also includes one or more detectors, apertures, etc., and an ion beam blanker.

  [30] The liquid metal ion source 20 includes a reservoir 21 that maintains liquid metal and a tip 22 that is heated by a filament current provided by a filament current supply device 23. The tip 22, and alternatively the reservoir 21, is also heated. The metal is maintained in liquid form. The reservoir and tip are arranged to form a liquid metal film at tip 22. An electric field induced by an electrode such as extraction electrodes 30 and 40 extracts ions from the apex of tip 22.

  [31] The FIB system 10 also includes an ammeter 102 electrically connected to the extraction electrode 30 to provide an approximate current value for ions extracted from the tip 22 to the processor 104. Note that the ammeter may be electrically coupled to other power sources or portions of the system 10. The processor 104 is electrically connected to the ammeter 102 and can control the liquid metal ion source 20.

  [32] FIG. 2 illustrates a method of controlling a liquid metal ion source. The method 120 begins at step 122 where the FIB system is started. Step 122 may include heating the liquid metal ion source 20, stabilizing ion emission from the liquid metal ion source 20, calibrating ion optics, and the like. The step of calibrating may include the reduction of optical aberrations and the placement of ion optics.

  [33] To simplify the explanation, at the end of step 122, it is assumed that the liquid metal ion source 20 is in active mode operation (as illustrated by box 123 located between steps 122 and 124). Has been. Thus, the ions are extracted to form a focused ion beam, which can be used for various purposes, such as alternately carving an object and generating a FIB image.

  [34] Step 122 is followed by step 124 of detecting the need to change the operating mode to idle mode. The detection may be based on a request from an operator of the FIB system, but may be generated as a response state of the FIB system. For example, it may be required if the liquid metal ion source has not been used to generate the FIB image for a certain time interval from the mode treatment.

  [35] Step 124 is followed by step 126 which performs a transition between active and idle modes. Step 126 may include pre-transition steps such as deactivating the automatic source stabilization process and preserving the extraction electrode voltage level. These pre-transition measures are followed by a step of lowering the extraction electrode voltage level. Conveniently, the extraction electrode voltage level is lowered to a level below the non-extraction ion level by a first voltage difference. The inventor has used a FIB system where the unextracted ion level is about 6500V and the voltage level can be lowered to 6300V.

  [36] At step 126, the system is in idle mode operation, as illustrated by the box stops located between step 126 and step 128.

  [37] Step 126 is followed by step 128 of detecting the need to change the operating mode to active mode.

  [38] Step 128 is followed by step 130 of performing a transition to active mode. The transition includes increasing the extraction electrode voltage to the level stored in step 128. Step 130 may also include a post-transition step that changes the voltage level of the suppression electrode to provide a stable flow of extracted ions at a predetermined current level. The inventor has stabilized the liquid metal ion source at the 2 micron ampere level. The step after the transition may also include a step of changing the voltage level of the extraction electrode in order to prevent the suppression voltage from reaching the upper limit value or the lower limit value of the voltage.

  [39] Step 130 is followed by step 124.

  [40] Once the liquid metal ion source is maintained in active mode for an extended time interval, the suppression voltage is gradually increased to provide the same current level. This increment is limited by the performance of the power supply connected to the suppression electrode. Once this occurs, the FIB system must be shut off and a high current consumption heating process begins. This substantially shortens the lifetime of the liquid metal ion source. It should be noted that the above change in the voltage level of the suppression electrode can be replaced by or achieved by a change in the extraction voltage.

  [41] The inventors have found that the transition between idle mode and active mode also provides a good extracted voltage / radiated current level ratio. The transition substantially resets the extraction voltage level increment, thus eliminating the current waste associated with the heating process.

  [42] FIG. 3 shows various operating modes (bottom curve labeled “Ext.c”), extracted electrode voltage level (upper curve labeled “Ext. V”), suppression electrode voltage level. 3 illustrates three curves showing the current extracted in (intermediate curve labeled “Sp. V”). The upper curve shows that during the active mode, the extraction electrode voltage level is in the first range, which is higher than the voltage level included in the third range of voltage levels provided during the idle mode. Illustrates including levels. The middle curve shows that during the active mode, the suppression electrode voltage level is in the second range, which is higher than the voltage level included in the fourth range of voltage levels provided during the idle mode. Illustrates including levels.

  [43] It will be apparent to those skilled in the art that the disclosed subject matter can be modified in many ways and many embodiments can be envisioned other than the specifically described and described forms. .

  [44] Accordingly, the above disclosed subject matter is exemplary, not limiting, and includes all variations and other modifications that fall within the true spirit and scope of the present invention, to the maximum extent permitted by law. The appended claims are intended to cover the embodiments.

  [45] The scope of the invention is to be determined by the broadest possible interpretation of the equivalents rather than the appended claims and the above specification.

[26] FIG. 1 is a schematic description of an FIB system according to an embodiment of the present invention. [27] FIG. 2 is a flowchart illustrating a method for controlling liquid metal ions. [28] FIG. 3 illustrates various voltage levels during an exemplary continuous transition between active mode operation and idle mode operation, according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Liquid metal ion source, 21 ... Reservoir, 22 ... Tip, 23 ... Filament current source, 30 ... Extraction electrode, 32 ... Extraction power source, 40 ... Suppression electrode, 42 ... Suppression power source, 55 ... Aperture, 60 ... Ion beam deflector, 102 ... Ammeter, 104 ... Processor.

Claims (30)

A method for controlling a liquid metal ion source comprising a tip, a first electrode and a second electrode , comprising:
Metal ions formed at the tip of the liquid metal ion source while maintaining the first electrode in the first voltage level range and maintaining the second electrode in the second voltage level range and during the active mode operation of the liquid metal ion source the method comprising the steps of: extracting,
Maintaining the first electrode in a third voltage level range, maintaining the second electrode in a fourth voltage level range, and substantially extracting metal ions from the tip during idle mode operation of the liquid metal ion source and step be reduced to,
Including
At least one of the third voltage level range and said fourth voltage level range does not include the zero voltage level,
Wherein the first voltage level range Unlike the third voltage level range,
The upper end of the fourth voltage level range is higher in absolute value than the upper end of the second voltage level range;
A method characterized by that .   The method of claim 1, wherein the first electrode is an extraction electrode. The method of claim 1 , wherein an upper end of the first voltage level range is higher in absolute value than an upper end of the third voltage level range. The third voltage level range, the absolute value has a lower voltage level than the first by a voltage difference between the non-extracted voltage level at A method according to claim 1.   The method of claim 1, wherein the transition between the idle mode and the active mode does not substantially change ion optical properties of ion optics located downstream of the liquid metal ion source.   The method of claim 1, wherein the transition between the idle mode and the active mode is rapid. The method of claim 6 , wherein the transition between the idle mode and the active mode does not substantially change ion optical properties of ion optics located downstream of the liquid metal ion source. The method of claim 6 , wherein the transition between the idle mode and the active mode is rapid.   The method of claim 1, wherein the transition between the idle mode and the active mode is shorter than one minute.   The method of claim 1, wherein the first electrode is a suppression electrode.   The method of claim 1, wherein there is no ion release from the tip during the idle mode. Wherein in the idle mode, ions supplied to the tip is maintained in liquid form, the method according to claim 1. Wherein after the transition between the idle mode and the active mode, the step of stabilizing the ion extraction from the tip is followed, the method of claim 1. Wherein the step of stabilizing, by measuring the ion current extracted from the tip, and, that, to change the voltage level of the voltage supplied to at least one of the first electrode and the second electrode 14. The method of claim 13, comprising . The transition between the idle mode and the active mode does not include the step of heating the liquid metal ion source, The method of claim 1. A liquid metal ion source ,
The tip ,
A first electrode and a second electrode ;
Wherein the second voltage level range to maintain said first electrode at a first voltage level range to extract metal ions formed during active mode operation at the tip of the liquid metal ion source before Symbol liquid metal ion source In order to maintain the second electrode, the first electrode is further maintained at a third voltage level range to substantially reduce metal ion extraction from the tip during idle mode operation of the liquid metal ion source. to maintain the second electrode at a fourth voltage level range, and a controller coupled to the at least one power supply,
With
Free of at least one of a zero voltage level of said third voltage level range and said fourth voltage level range,
The first voltage level range Unlike the third voltage level range,
The upper end of the fourth voltage level range is higher in absolute value than the upper end of the second voltage level range;
A liquid metal ion source. The liquid metal ion source according to claim 16 , wherein the first electrode is an extraction electrode. 18. The liquid metal ion source according to claim 17 , wherein an upper end of the first voltage level range is higher in absolute value than an upper end of the third voltage level range. The third voltage level range, only the first voltage difference in absolute value with the non-extracted voltage lower voltage level than the level, the liquid metal ion source according to claim 17. The transition between the idle mode and the active mode does not substantially change the ion optical properties of the ion optics located downstream of the liquid metal ion source, a liquid metal ion source according to claim 17. The transition between the idle mode and the active mode is rapid, the liquid metal ion source according to claim 16. The transition between the idle mode and the active mode does not substantially change the ion optical properties of the ion optics located downstream of the liquid metal ion source, a liquid metal ion source according to claim 16. The transition between the idle mode and the active mode is rapid, the liquid metal ion source according to claim 22. The liquid metal ion source of claim 16 , wherein the transition between the idle mode and the active mode is shorter than 1 minute. The liquid metal ion source according to claim 16 , wherein the first electrode is a suppression electrode. The liquid metal ion source of claim 16 , wherein there is no ion emission from the tip during the idle mode. Wherein in the idle mode, ions supplied to the tip is maintained in liquid form, a liquid metal ion source according to claim 16. The liquid metal ion source of claim 16 , wherein the controller can begin a stabilization process after transition between the idle mode and the active mode. The stabilization process is to measure the ion current extracted from the tip, and, the step of changing the voltage level of the voltage supplied to the at least one electrode of said first electrode and said second electrode 30. The liquid metal ion source of claim 28 . The transition between the idle mode and the active mode does not include the step of heating the liquid metal ion source, a liquid metal ion source according to claim 28.

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